Recently, the market for a therapeutic monoclonal antibody has been grown very fast, and the productivity has increased sharply. Particularly, the development in cell line engineering technology and cell culturing technology increases the titer of culture solution to 10 g/L at a commercial scale.
In general, the chromatographic method used most-frequently for purifying the monoclonal antibody (mAb) in a biopharmaceutical field, includes the three steps of: 1) a protein A chromatography capturing selectively the mAb in the cell culture solution, 2) a cation exchange resin chromatography performed as a second step; and 3) an anion exchange resin chromatography as a final purification step (FIG. 1).
The protein A chromatography achieves a yield of 90% or higher and a purity of 99% or higher at a reference with Size Exclusion Chromatography (SEC) at only one purification time, because it has a very strong affinity to the mAb in the cell culture solution. Thus, the method is the most powerful tool for purifying the mAb using the chromatography.
The bottle neck step in the production of therapeutic mAb using the cell culture with a high titer lies in the purification step, more specifically protein A chromatography which has the following disadvantages due to the traditional batch-type operation:
1) The commercially-available protein A resin is very expensive and has very shorter life cycle than the other resin due to the use of protein as a ligand. When it operates in a batch-type, the packed resin is only used as about 30 to 50% due to the limited kinetics of the protein. The method requires about two or three times of column volume as that operated in equilibrium state;
2) Only one column is used in a batch-type and the steps of equilibrium, sample injection, washing, elution, regeneration and sterilization are carried out sequentially. The batch-type method requires relatively longer processing time and thus shows very low batch processing speed (FIGS. 2); and
3) The washing and elution steps need considerably large volume of buffer solution in the batch-type chromatography, but the buffer solution is made of water for injection, thereby causing an economical burden.
To solve the disadvantages of the batch-type chromatography and the problems caused by the high titer in the cell culture, there are recently various attempts to study the application of the Simulated Moving Bed (SMB) chromatography to the production of the therapeutic antibody.
SMB chromatography has been used largely for the petrochemical and the mineral field. Compared with the batch-type chromatography, SMB chromatography has various advantages such as a small volume of consumed buffer solution, a high productivity and a high concentration of the final product, and recently, has been actively studied for applying to the separation of biomaterials.
To apply SMB chromatography to the purification of bioengineering products, especially a protein, there are some problems to be previously settled as follows:
1) The loss of product is inevitable at an initial starting operation and final closing process of SMB chromatography. When it is applied for the production of product in a short campaign, the product loss is relatively higher than the batch-type chromatography;
2) It is difficult to define the batch which is very important for the production of biopharmaceuticals. In particular, the division of batch is basically difficult in the purification method which maintains the efficiency by continuously operating the cell culture according to the process principle;
3) It is not suitable for the process to produce various products for a short campaign. Generally, SMB chromatography uses at least four columns, and the patent owned by Biogen Idec uses at most twenty columns. There are some works for product change over in order to prevent the cross-contamination of the products in the transition step that the operation for the next product campaign cannot start, after the operation of previous product campaign terminates. The works include the change of all used parts made from rubber and plastic, and the preparation of the homogeneously packed column by changing the resin. Because SMB chromatography apparatus is very complex and employs many columns, a long time and a large labor are required for the transition step.
4) The mobile phase of SMB chromatography employs many columns, pumps and valves, which are controlled by the complex control system. It is difficult to stably maintain the operation parameters due to the troubles with the pumps or valves.
U.S. Pat. No. 7,220,356 and Comparison of protein A affinity sorbent II Mass Transfer properties, Alios Jungbauer et al, Journal of chromatography A, 1093(2005) pp.98-110 are provided as the references.